MEMS device with getter layer

Abstract

A MEMS device comprises a first layer ( 1 ), a second layer ( 2 ) and a third layer ( 3 ) sealed together. A mobile structure ( 7.1, 7.2 ) in the second layer ( 2 ) is defined by openings ( 8.1, 8.2 ) in the second layer ( 2 ). In the first layer ( 1 ), there is at least one first-layer cavity ( 6.1, 6.2 ) with an opening towards the mobile structure ( 7.1, 7.2 ) of the second layer ( 2 ). In the third layer ( 3 ), there is at least one third-layer cavity ( 9 ) with an opening towards the mobile structure ( 7.1, 7.2 ) of the second layer ( 2 ). Therefore, the third-layer cavity ( 9 ) and the second layer ( 2 ) define a space within the MEMS device, A getter layer ( 10.1, 10.2 ) arranged on a surface of said space. The getter layer ( 10.1, 10.2 ) is preferably arranged on a surface of the second layer ( 2 ) and in particular, the getter layer ( 10.1, 10.2 ) is arranged on a static part of the second layer ( 2 ). Alternatively, the MEMS device has a third-layer cavity ( 24 ) with at least two recesses ( 25.1, 25.2, 25.3 ) and the getter layer ( 26.1, 26.2, 26.3 ) is arranged on a surface of the recesses ( 25.1, 25.2, 25.3 ).

The invention claimed is: 
     
       1. A MEMS device comprising:
 a) a first layer, a second layer and a third layer sealed together, 
 b) a mobile structure in the second layer defined by openings in the second layer, 
 c) in the first layer at least one first-layer cavity with an opening towards the mobile structure, 
 d) in the third layer at least one third-layer cavity with an opening towards the mobile structure, wherein the third-layer cavity and the second layer define an inner surface enclosing a space within the MEMS device, 
 e) at least one getter layer arranged on said inner surface, 
 wherein the third-layer cavity is larger than the mobile structure and includes recesses that are smaller than the mobile structures. 
 
     
     
       2. A MEMS device according to  claim 1 , wherein the at least one getter layer is arranged on a surface of the second layer. 
     
     
       3. A MEMS device according to  claim 2 , wherein the at least one getter layer is arranged on a static part of the second layer. 
     
     
       4. A MEMS device according to  claim 3 , wherein the third-layer cavity has at least two recesses and wherein at least two getter layers are arranged on a surface of said recesses. 
     
     
       5. A MEMS device array comprising at least two MEMS devices according to  claim 4 , wherein the recesses are outside a cavity for housing the mobile structure. 
     
     
       6. A MEMS device according to  claim 1 , wherein the second layer is a semiconductor on insulator (SOI) layer. 
     
     
       7. A MEMS device according to  claim 1 , wherein the first layer comprises conductive structures penetrating the first layer. 
     
     
       8. A method for manufacturing a MEMS device, comprising the steps of:
 a) providing three layers, wherein a first layer of said three layers has at least one first-layer cavity, a second layer has openings for defining a mobile structure and a third layer has at least one third-layer cavity, 
 b) sealing the three layers together for providing at least one sealed inner space, in such a way that the first-layer cavity and the third-layer cavity have their opening towards the mobile structure of the second layer, 
 c) prior to sealing the three layers together at least one getter layer is provided on said inner surface, 
 wherein the third-layer cavity is larger than the mobile structure and includes recesses that are smaller than the mobile structures. 
 
     
     
       9. A method according to  claim 8 , wherein the layers have several mobile structures, several first-layer cavities and several third-layer cavities and therein the three layers are sealed together for providing a plurality of sealed inner spaces. 
     
     
       10. A method according to  claim 9 , wherein the sealed layers are cut into chips, each chip containing at least one mobile structure. 
     
     
       11. A method according to  claim 8 , wherein the at least one getter layer is arranged on a surface of the second layer. 
     
     
       12. A method according to  claim 8 , wherein the third-layer cavity has at least two recesses and wherein at least two getter layers are arranged on a surface of said recesses.